From commercial direct marketing, a lesson in envelope design.
Here's the front. Not too promising. They don't even care who gets it, as long as they're at this address. Yawn.
I'm about to recycle it. But then I turn it over and see the back:
Whoa! It suddenly got a lot more interesting! Who'd throw away actual money?
Every envelope has two sides. Both are likely to be see, even by recipients who mean to throw the piece away. And if they're even considering opening it, they'll spend more time looking at the back than the front.
Use both sides for best direct mail results!
(Reality check: They wanted me to fill out a survey about my TV viewing habits. Back to yawn. I didn't respond. Oh well.)